1. Field of the Invention
The present invention relates generally to radio frequency identification (RFID) devices, and more specifically relates to communications between RFID tags and a reader.
2. Discussion of the Related Art
Radio-frequency identification (RFID) is the use of an object (typically referred to as an RFID tag) applied to or incorporated into a product, animal, or person for the purpose of identification and tracking using radio waves. Some tags can be read from several meters away and beyond the line of sight of the reader. A conventional RFID system includes a reader or interrogator and one or more tags. The reader can transmit wireless signals to the tag/s, and the tag/s can transmit wireless signals to the reader. Wireless signals from a tag contain a tag identification code that uniquely identifies the particular tag that produced these wireless signals.
Most RFID tags contain at least two parts. One is an integrated circuit for storing and processing information, modulating and demodulating a radio-frequency (RF) signal, and other specialized functions. The second is an antenna for receiving and backscattering the signal. There are generally three types of RFID tags: active RFID tags, which contain a battery and can transmit signals autonomously, passive RFID tags, which have no battery and require an external source to provoke signal transmission and battery assisted passive (semi-passive) which require an external source to wake up but have significant higher forward link capability providing great read range.
There are a variety of factors that can degrade or prevent communication between the reader and a tag. As one example, if the tag is too far from the reader, the signal received at the tag will no longer contain enough energy to power the tags internal circuitry. As another example, the tag may be suitably close to the reader, but may be oriented in such a way that it cannot absorb enough energy from the received signal to power its internal circuitry. As yet another example, there may be an object disposed between the reader and the tag that absorbs or reflects the wireless signal transmitted by the reader, such that by the time the signal gets to the tag, the signal does not have enough remaining energy to power the internal circuitry of the tag.